American Geophysical UnionOS52B-04, 19 December 2014San Francisco, CA

A Cross-hole, Multi-year Tracer Injection Experiment in the Volcanic Ocean Crust

A. T. Fisher1, N. Neira2, C. G. Wheat3, J. Clark2, D. Winslow1, K. Becker4, C.-C. Hsieh5, M. Rappé5

1Earth and Planetary Sciences Department and Center for Dark Energy Biosphere Investigations University of California, Santa Cruz2University of California, Santa Barbara3University of Mississippi4University of Miami, RSMAS5University of Hawaii

modified from Fisher and Wheat (2010)

The upper oceanic crust is a hydro-thermo-chemo-bio reactor

The Hydrogeologic Architecture of Basaltic Oceanic Crust: Hydrogeology, Geochemistry, Microbiology

Focus on active ridge-flank processes to resolve:

• Magnitude and nature (distribution, extent of channeling) of permeability in crustal fluid-rock systems, variations, scaling (temporal, spatial)

• Magnitudes and directions of driving forces, fluid fluxes, flow channeling, and associated solute, heat, and microbial transport and storage

• Relations between fluid flow, compartmentalization, microbiological communities, seismic properties, alteration, and structure

• Nature of distinct fluid reservoirs, fluid residence times and velocities, response to transient perturbations

Scientific Ocean Drilling Experiments

modified from Fisher et al. (2011a)

IODP Expeditions 301 (2004) and 327 (2010), ROV/HOV expeditions (2004-14)

Subseafloor borehole observatories (CORKs)

• Seal reentry hole to prevent hydrologic contamination, allow return to pre-drilling P/T/Chemistry/MBIO conditions

• Allow access to the subseafloor environment over long times, without drillship

• Permit passive monitoring, facilitate active testing

• Isolate multiple depth intervals

Sounds like a lot of work... It is! But it’s worth the effort…

Hu

ndr

ed

s o

f met

ers

modified from Fisher et al. (2011b)

Setting up a Cross-hole Experiment

• New CORKs installed in Holes 1026B, 1301A/B during IODP Expedition 301 (2004)

• New CORKs installed in Holes 1362A/B during IODP Expedition 327 (2010)

• CORK in Hole 1027C rehabilitated with on AT18-07 (2011)

P

P

Basement relief

modified from Fisher et al. (2011a)

• Tracer injected 2010

• Monitor seafloor (2010-14)

• Monitor downhole (2010-14)

Tracer:• Sulfur Hexafluoride (SF6)

• Injected ~23 M in 24 hr

• Injectate [SF6] ~ 48 µM

• Detection limit ~ 1 pM (dilution factor = 5 x 107)

Fisher et al. (2011b)

First controlled measurement of water, solute velocity!

Setting up a Cross-hole Experiment

Inferred flow direction: N20E, based on geochem, heat flow, modeling

Tracer testing concepts

modified from Fisher et al. (2011b)

Tracer Test Configuration and Operations

Hole 1362BOne depth intervalInjection (2010)Wellhead OS (2011, 13, 14)Downhole OS (2014)Free flow ≥2011

100

0 m

Hole 1301A

Hole 1362A

Hole 1026B

Tracer Test Configuration and Operations

Hole 1362B

100

0 m

Hole 1362A

Hole 1026B

Hole 1301AOne depth intervalWellhead OS (2010, 11, 13, 14)Discharging CORK!

Tracer Test Configuration and Operations

Hole 1362B

100

0 m

Hole 1362ATwo depth intervalsWellhead OS (2011, 13, 14)Downhole OS (2014)

Hole 1026B

Hole 1301A

Tracer Test Configuration and Operations

Hole 1362B

100

0 m

Hole 1362A

Hole 1026B

Hole 1301A

One depth intervalWellhead OS (2010-11,13,14)Downhole OS (2014)

Tracer Recovery: Hole 1301A

Hole 1301A(discharging)

Hole 1362B

Hole 1362A

Hole 1026B

1000

m

modified from Neira (2014)

Expedition delayed (2012)

Tracer Recovery: Hole 1301A

modified from Neira (2014)

Expedition delayed (2012)

SF6 peak arrival~1 m/day

Long plume tail, low [SF6]…

Tracer Recovery: Hole 1362B

modified from Neira (2014)

Hole 1301A(discharging)

Hole 1362B

Hole 1362A

Hole 1026B

1000

mRaw

Corrected

Flowmeter attached,

Valve opened, Wellhead sampler deployed

Expedition delayed (2012)

Tracer Recovery: Hole 1362A

modified from Neira (2014)

Hole 1301A

Hole 1362B

Hole 1362A

Hole 1026B

1000

m

Valve opened

(1362B), Wellhead sampler deployed

Expedition delayed (2012)

Tracer Recovery: Hole 1026B

modified from Neira (2014)

Hole 1301A

Hole 1362B

Hole 1362A

Hole 1026B

1000

m

2010-13Wellhead

Tracer Recovery: Hole 1026B

modified from Neira (2014)

2010-13Wellhead

Tracer Recovery: Hole 1026B

modified from Neira (2014)

Hole 1301A

Hole 1362B

Hole 1362A

Hole 1026B

1000

m

2010-13Wellhead

SF6 peak arrival≥1 m/day

The first three-dimensional, coupled fluid-heat flow ridge-flank hydrothermal models

• Field data guide model design, constrain results (hydrogeological, thermal, chemical)

• Small outcrop vents 5-20 kg/s, 1-2 MW power

• No regional mining of crustal heat

• Basement fluids at 65°C, highly altered

modified from Winslow and Fisher (2014)

The first three-dimensional, coupled fluid-heat flow ridge-flank hydrothermal models

Mixed convection and a hydrothermal siphon between outcrops…

modified from Winslow and Fisher (2014)

tThe first three-dimensional, coupled fluid-heat flow ridge-flank hydrothermal models

Mixed convection and a hydrothermal siphon between outcrops…

modified from Winslow and Fisher (2014)

Specific discharge x 10-8 (m/s)0 0.4 0.8 1.2 1.6

Cou

nt

2,000

6,000

10,000

14,000

0.13 0.26 0.38Specific discharge (m/yr)

Flow rates in the upper ocean crust, between outcrops, are about

0.2 m/yr

What do different flow rates imply?

• Tracer tests: vL ~350 m/yr

• Thermal data/models: q ~0.2 m/yr

• Effective porosity (fraction of rock with flowing fluid):

ne = q/vL = (0.2)/350 ~ 0.0005 (0.05%)

• Implications: very heterogeneous flow system, low specific surface

area available for reaction, most pores are dead ends, etc.

Moreno and Tsang, 1994Tsang et al., 1991

What do different flow rates imply?

• Tracer tests: vL ~350 m/yr

• Thermal data/models: q ~0.2 m/yr

• Effective porosity (fraction of rock with flowing fluid):

ne = q/vL = (0.2)/350 ~ 0.0005 (0.05%)

• Implications: very heterogeneous flow system, low specific surface

area available for reaction, most pores are dead ends, etc.

What do different flow rates imply?

• Tracer tests: vL ~350 m/yr

• Thermal data/models: q ~0.2 m/yr

• Effective porosity (fraction of rock with flowing fluid):

ne = q/vL = (0.2)/350 ~ 0.0005 (0.05%)

• Implications: very heterogeneous flow system, low specific surface

area available for reaction, most pores are dead ends, etc.

What do different flow rates imply?

• Tracer tests: vL ~350 m/yr

• Thermal data/models: q ~0.2 m/yr

• Effective porosity (fraction of rock with flowing fluid):

ne = q/vL = (0.2)/350 ~ 0.0005 (0.05%)

• Implications: very heterogeneous flow system, low specific surface

area available for reaction, most pores are dead ends, etc.

Preliminary Interpretations

• We can run tracer injection tests in the ocean crust!

• Dominant flow direction is N20E, as hypothesized.

• Dissolved gas tracer transport rate is ~1 m/day.

• Effective porosity for tracer transport is small <<1%.

• Upper crustal aquifer is highly heterogeneous

“most of the aquifer is not an aquifer”

Preliminary Interpretations

• More data and interpretations from 1000s of samples recovered

(wellhead/downhole) in Summer 2014, ongoing/new modeling, links to

microbiological analyses…

• Data to be analyzed from cross-hole pressure and temperature

response, independent estimates of formation permeability…

• We can run tracer injection tests in the ocean crust!

• Dominant flow direction is N20E, as hypothesized.

• Dissolved gas tracer transport rate is ~1 m/day.

• Effective porosity for tracer transport is small <<1%.

• Upper crustal aquifer is highly heterogeneous

“most of the aquifer is not an aquifer”

Acknowledgements

J. Cowen, E. Davis, K. Edwards, C. Gable, S. Hulme, G. Iturrino, M. Hutnak, W. Kirkwood, T. Pettigrew, V. Spiess, P. Stauffer, T. Tsuji, T. Urabe, H. Villinger, L. Zühlsdorff, and many others…

Collaboration, advice, encouragement:

Funding, leadership, trust:Planning, field support:

IOs for ODP and IODP, crews and technicians of: J. Resolution, Atlantis, Thompson, Alvin, Jason, ROPOS…

Thank you!

Questions?

modified from Fisher (2005)

Thank you!